From PICLIST@MITVMA.MIT.EDU Fri Nov 15 17:37:46 2002 Received: from cherry.ease.lsoft.com [209.119.0.109] by dpmail10.doteasy.com with ESMTP (SMTPD32-7.13) id A16A3FB0148; Fri, 15 Nov 2002 17:37:46 -0800 Received: from PEAR.EASE.LSOFT.COM (209.119.0.19) by cherry.ease.lsoft.com (LSMTP for Digital Unix v1.1b) with SMTP id <0.007DE4AA@cherry.ease.lsoft.com>; Fri, 15 Nov 2002 20:23:36 -0500 Received: from MITVMA.MIT.EDU by MITVMA.MIT.EDU (LISTSERV-TCP/IP release 1.8d) with spool id 2423 for PICLIST@MITVMA.MIT.EDU; Fri, 15 Nov 2002 20:23:25 -0500 Received: from MITVMA (NJE origin SMTP@MITVMA) by MITVMA.MIT.EDU (LMail V1.2d/1.8d) with BSMTP id 6554; Fri, 15 Nov 2002 20:21:39 -0500 Received: from ginger.grouptel.net [216.243.47.2] by mitvma.mit.edu (IBM VM SMTP Level 320) via TCP with ESMTP ; Fri, 15 Nov 2002 20:21:38 EST X-Comment: mitvma.mit.edu: Mail was sent by ginger.grouptel.net Received: from K6III450 (host88.FASTdial.net [216.243.8.88]) by ginger.grouptel.net (8.12.2/8.12.2) with SMTP id gAG1LaCo016581 for ; Fri, 15 Nov 2002 20:21:38 -0500 (EST) MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook IMO, Build 9.0.2416 (9.0.2911.0) X-MimeOLE: Produced By Microsoft MimeOLE V5.50.4133.2400 Importance: Normal Message-ID: Date: Fri, 15 Nov 2002 20:21:14 -0500 Reply-To: pic microcontroller discussion list Sender: pic microcontroller discussion list From: Paul Hutchinson Subject: Re: [EE]:Pressure sensor confusion To: PICLIST@MITVMA.MIT.EDU In-Reply-To: X-RCPT-TO: Status: R X-UIDL: 277600758 X-Evolution-Source: pop://mailinglist%40farcite.net@mail.farcite.net/ X-Evolution: 000007b8-0000 I like to use dedicated math software such as MathCAD, Mathematica, Maple, etc. to perform the regressions quickly. http://www.mathsoft.com/ http://www.wolfram.com/ http://www.maplesoft.com/ They have built-in regression functions to handle any kind of curve fitting you would ever need. The problem with these types of programs are the learning curves and prices ($500.00 to $5000.00). 15 or so years ago I used was a nice little DOS freeware program named "Splot" that worked well for polynomial regressions. There may be some good modern alternatives available from university sites although they are probably only available for Unix platforms. IIRC the Maple package originated at the University of Toronto. I just Googled on: software "polynomial regression" and found these possibly helpful links: http://www.analyse-it.com/polynomial-regression_y.htm http://www.curvefit.com/index.htm For the actual base equation type, I've had the best luck in using the Steinhart-Hart equations for modeling thermistor resistance vs. temperature. http://www.betatherm.com/stein.html Paul > -----Original Message----- > [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of llile@SALTONUSA.COM > Sent: Friday, November 15, 2002 3:55 PM > Subject: Re: [EE]:Pressure sensor confusion > > That's one way to deal with it. > > A typical problem for me is interpolating thermistor data. The thermistor > curve comes in chart form from the manufacturer, in very un-handy > increments. It's quite a complex curve, and I think curve fitting it > would be a long involved task (unless Excel does this automatically > somehow? ) Linear curve fitting would be a cinch. The only way I know > how to curve fit a nonlinear is, guess at the type of equation to use, > plot it next to your data, sum the squares of the differences, then run a > linear regression on the results and use a Tools:GoalSeek on the results > to approach the minimum, then guess again at the type of equation to use > until you like the fit.. It is a time-consuming process, usually. > > Is there a more efficient way? > > > -- Lawrence Lile > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.